So why are all my maxed out cities of each race suddenly having the walls dissapear?

I have a maxed out desert orc , alpine human, and alpine elf city..... when i logged in today to check on them i noticed that the orc city has lost almost all of its walls and whatever is left is buggier than HELL and the elf and human cities are not far behind.... whats the deal with this?

I click repair walls and it just starts building crap all over again for full price... kinda ****ed that now that i actually get some time to try city sieges with my cities that have been maxed out since the first night of release I can't even do anything because of this horrible bug.